This invention relates to a jacket for rotatable magnetic recording medium and more particularly to a protective structure for the jacket which can prevent dust from entering the jacket.
Rotatable magnetic sheets (generally known as floppy discs) are widely used as media for magnetic recording and reproducing in recent years. These rotatable magnetic sheets are usually sheathed in a package (referred to as a jacket hereinafter) provided with internal liners made of non-woven fabric. The jacket has an opening at the center thereof for rotating the magnetic sheet, an opening for contacting the rotatable magnetic sheet with a magnetic head and an opening for displaying sectors. Dust in the air tends to enter the jacket through these openings to contaminate the surface of the magnetic sheet, and cause errors.
Such a jacket is usually placed in an envelope for protecting it mainly from such dust. However, as such an envelope covers only two thirds or three fourths of the surface of the jacket and is not closely attached to said opening of the jacket, dust in the air cannot be fully prevented from entering the jacket into the envelope.
Moreover, the jacket is taken out from the envelope when a user wishes to use the rotatable magnetic sheet therein, and the user tends to throw away the envelope. The openings of a jacket are often exposed to the air when such sheet is stored for a long time.
The material of such an envelope was mainly made of natural paper in the prior art, but recently they are often made of synthetic paper such as of polyethylene (e.g. TYVEK Manufactured by DuPont).
When we consider cost-wise a product comprising a rotatable magnetic sheet, a jacket and a protective envelope, the cost of the envelope is by no means negligible and it is not quite effective in preventing dust.